Many industries use die cutting, laser cutting, printing, embossing, or stamping to create a series of patterns on a continuous strip of material or web of material by passing the material between a pair of cooperatively rotating cylinders including a rotary die cylinder of a rotary die. This technique may be used, for example, to cut holes or other patterns onto a printed strip of material at desired locations relative to indicia printed thereon. When the patterns are positioned at specific locations relative to each other or relative to pre-applied indicia, the patterns are said to be “in registration.”
Registration may be achieved with a controller or other control device. The controller maintains a die cut at the same interval as the repeat of patterns and/or indicia on the strip of material. To initially line up the die and patterns applied on the strip of material, an operator offsets a registration target position, which shifts the die patterns up or down the strip of material, effectively lining up the intervals of the strip of material and the die. However, the strip of material can move or slip out of alignment with the rotary die due to factors like a natural camber of the material, splices which may affect the material, other material properties, discrepancies introduced due to previous operations to the strip of material, etc. If one of the patterns is not positioned precisely at the desired location on the strip of material, a “registration error” occurs. One type of registration error may occur in the machine direction, or in the direction of movement of the strip of material, along an X-axis. A second type of registration error may occur in a direction perpendicular to the X-axis, in a side-to-side direction relative to the strip of material along a Y-axis. A third type of registration error may occur if the strip of material and/or the rotary cylinders of the rotary die are not angled correctly about a theta axis T, which is perpendicular to both the X-axis and the Y-axis.
Manual methods for determining registration errors for each pattern applied to the strip of material are too time-consuming for mass production operations. Prior art automated methods of measuring and calculating registration errors involve complex and/or numerous equations and compare statements, which can slow the processing time and the processing capability needed to determine the registration errors and correct for them “on the fly” or in a substantially continual manner for each pattern.
Accordingly, there is a need for a method and apparatus for correcting registration errors that overcomes the limitations of the prior art.